This invention relates to ethylene-carbon monoxide and more particularly to an improved process for preparing ethylene-carbon monoxide copolymers.
Ethylene-carbon monoxide copolymers have been known for several years and have been of considerable interest because of their potential value as engineering plastics. Ethylene-carbon monoxide copolymers having high carbon monoxide contents, particularly 40% or more, are especially interesting because they possess high melting points and other superior properties which would make them very suitable for many engineering applications. Ethylene-carbon monoxide copolymers are also of interest since carbon monoxide is a very inexpensive by-product obtained in the manufacture of steel and is, therefore, unlike most other monomeric materials used in the production of synthetic polymers, not derived from petroleum. In spite of the great potential of these copolymers, their development has been slow and they have not yet gained commercial acceptance. The principal reason for this is that no commercially feasible process for their production has been developed.
The preparation of high molecular weight ethylene carbon-monoxide copolymers has been accomplished by gamma radiation initiation but this method requires the use of expensive equipment, high pressures, and inordinately long reaction times. Furthermore, polymer produced by this method may be partially cross-linked and, thus, very difficult to process. Since chemical catalysis offers more advantages and fewer hazards than radiation initiation, considerable effort has been made to develop useful chemical catalytic process for the production of ethylene-carbon monoxide copolymers.
U.S. Pat. No. 2,495,286, issued to Brubaker, discloses the use of organic peroxides as catalysts for the preparation of ethylene-carbon monoxide copolymers. As shown in this patent and other patents such as the Nozaki patents, U.S. Pat. No. 3,689,460 and 3,694,412, very high pressures, onthe order of 500 atmospheres or more and high temperatures are required for the preparation of normally solid polymers when using peroxide catalysts. Furthermore, the total polymer yield and carbon monoxide content are quite low when the catalysts disclosed by Brubaker are used in the preparation of ethylene-carbon monoxide copolymers. This is unfortunate since it has been determined that ethylene-carbon monoxide copolymers having ethylene:carbon monoxide ratios close to unity have the most desirable physical properties and a higher degree of crystallinity than those containing lower carbon monoxide contents. It would be highly desirable to develop a process for preparing high melting ethylene-carbon monoxide copolymers in high yield and with high carbon monoxide contents without the necessity of resorting to the use of high pressures and temperatures.